Photocatalytic Conversion of Diluted CO2 into Tunable Syngas via Modulating Transition Metal Hydroxides

The conversion of diluted CO2 into tunable syngas via photocatalysis is critical for implementing CO2 reduction practically, although the efficiency remains low. Herein, we report the use of graphene-modified transition metal hydroxides, namely, NiXCo1–X-GR, for the conversion of diluted CO2 into syngas with adjustable CO/H2 ratios, utilizing Ru dyes as photosensitizers. The Ni(OH)2-GR cocatalyst can generate 12526 μmol g–1 h–1 of CO and 844 μmol g–1 h–1 of H2, while the Co(OH)2-GR sample presents a generation rate of 2953 μmol g–1 h–1 for CO and 10027 μmol g–1 h–1 for H2. Notably, by simply altering the addition amounts of nickel and cobalt in the transition metal composite, the CO/H2 ratios in syngas can be easily regulated from 18:1 to 1:4. Experimental characterization of composites and DFT calculations suggest that the differing adsorption affinities of CO2 and H2O over Ni(OH)2-GR and Co(OH)2-GR play a significant role in determining the selectivity of CO and H2 products, ultimately affecting the CO/H2 ratios in syngas. Overall, these findings demonstrate the potential of graphene-modified transition metal hydroxides as efficient photocatalysts for CO2 reduction and syngas production.